They came before DVD... I think they predate CD's, but I'm not completely familiar with the history. They're a type of digital movie format, pretty clean, but only NTSC resolution (Roughly half DVD size) and typically don't hold a very long length movie or whatever.
but only NTSC resolution (Roughly half DVD size)
half the size in terms of how much information/detail they will hold
even in places like Amazon.com, who hardly ever do region 2 videos and DVD's.
Or if you're really crazyhttp://www.amazon.co.jp